1. Field of the Invention
The present invention relates to an ultrasonic motor and an electronic apparatus using the ultrasonic motor, particularly to an ultrasonic motor increasing an output per unit volume and an electronic apparatus using the ultrasonic motor.
2. Description of the Related Art
In recent times, in the field of micromechanics, attention has been directed to realizing an ultrasonic motor utilizing flexing oscillation generated in a piezoelectric member applied with drive voltage such as an alternating current voltage as a power source thereof.
As an example of a conventional ultrasonic motor, there is provided, for example, an ultrasonic motor 100 of a circular plate type shown in FIG. 20 through FIG. 23B.
As shown by an outline sectional view of FIG. 20, the ultrasonic motor 100 is generally constituted by a piezoelectric element 101 in a circular plate shape, an oscillator 102 made of a metal as an elastic member adhered onto the piezoelectric element 101, a plurality of projections 103 erected integrally at an upper face of the oscillator 102 as the elastic member, enlarging displacement of oscillation of the piezoelectric element 101 and taking out an output thereof, a rotor 104 which is brought into contact with the projections 103 from above and rotating by way of frictional force by movement of the projections 103, a support shaft 105 penetrating centers of the piezoelectric element 101 and the oscillator 102, holding the piezoelectric element 101 and the oscillator 102 above a base plate 110 and playing a role of guiding rotation of the rotor 104 and a spring 106 for depressing a rotational center of the rotor 104 downwardly to thereby ensure predetermined contact pressure between the rotor 104 and the projections 103. In this case, the piezoelectric element 101 is applied with drive voltage via lead wires 107a and 107b crawling on the base plate 110.
According to the piezoelectric element 101, as shown by an outline upper view of FIG. 21, PZT which is a well-known piezoelectric material, is molded in a circular plate shape and is provided with a hole 101c for passing the rotating shaft 105 at its center and which is divided into six divisions in a circumferential direction and the divisions are polarized such that polarizing directions thereof are reverse to each other and each of the divisions is equally divided into two. As a result, there is constructed a constitution in which there are arranged a total of 12 pieces of polarized portions 101a polarized in positive polarity and polarized portions 101b polarized in polarity reverse thereto alternately at every two pieces thereof. Signs of plus (+) and minus (xe2x88x92) in the drawing represent polarities of polarization and in this case, polarizing treatment is carried out in the thickness direction of the piezoelectric element 101, plus (+) indicates that the polarizing treatment is carried out in a direction from the piezoelectric element 101 toward the oscillator 102 and minus (xe2x88x92) indicates that the polarizing treatment is carried out conversely in a direction from the oscillator 102 toward the piezoelectric element 101.
Here, as shown by schematic views of FIG. 21 and FIG. 22, the projections 103 are provided at every other boundaries of the polarized portions.
Further, the piezoelectric element 101 is provided with an electrode 108a connected to the lead wire 107a and an electrode 108b connected to the lead wire 107b as electrodes for inputting drive voltage. The electrode 108a covers every other polarized portions, mentioned above, further, the electrode 108b covers every other polarized portions reversely to the electrodes 108a. 
That is, when drive voltage is inputted to the electrode 108a, as shown by FIG. 23A, the piezoelectric element 101 is generated with a standing wave such that central portions of the respective polarized portions covered by the electrode 108a constitute antinodes. The projections 103 are disposed at every other intermediaries of the antinodes and nodes of the standing wave. Therefore, head portions of all of the projections 103 draw a locus in a circular arc shape and accordingly, in this case, as shown by an arrow mark in FIG. 23A, the rotor 104 is rotated in one direction. At this occasion, the projections 103 play a role of amplifying oscillation of the standing wave.
Further, when drive voltage is inputted to the electrode 108b, as shown by FIG. 23B, the piezoelectric element 101 is generated with a standing wave such that central portions of the respective polarized portions covered by the electrode 108b constitute antinodes and accordingly, the head portions of all of the projections 103 draw a locus in a circular arc shape in a reverse direction. Therefore, in this case, as shown by an arrow mark in FIG. 23B, the rotor 104 is rotated in a reverse direction.
However, according to the above-described ultrasonic motor 100, in order to switch the rotational direction, the ultrasonic motor is driven by selecting an electrode for applying the drive voltage from the electrode 108a or the electrode 108b. Therefore, not all of the polarized portions provided in the piezoelectric element 101 but a half thereof are driven.
That is, all of the piezoelectric elements 101 are not utilized simultaneously and accordingly, an output of the ultrasonic motor 100 is small in consideration of the size.
In view of the above-described situation, it is an object of the present invention to provide an ultrasonic motor increasing an output per unit volume by driving the ultrasonic motor by using all of polarized portions provided to a piezoelectric element and enabling regular and reverse rotation thereof, and an electronic apparatus having an ultrasonic motor utilizing the ultrasonic motor.
In order to resolve the above-described problem, according to the invention, there is provided an ultrasonic motor characterized in that in an ultrasonic motor comprising a piezoelectric element for generating an oscillation wave and a moving member driven by the oscillation wave generated by the piezoelectric element, the ultrasonic motor including the piezoelectric element in a circular disk shape having polarized portions divided by a multiple of four in a circumferential direction, projections provided at upper portions of and spaced apart by odd numbers of the polarized portions of the piezoelectric element for taking out motor drive force from standing wave oscillation generated by the piezoelectric element, and a moving member driven by the projections brought into contact with upper ends of the projections, polarities of each two adjacent polarized portions are the same and polarities of adjacent pairs are reverse to each other, a first polarized portion group constituted by every other polarized portion and a second polarized portion group constituted by the polarized portions not belonging to the first polarized portion group, selecting whether phases of alternating voltage inputted to the first polarized portion group and the second polarized portion group are made to be the same phase or to constitute a phase difference of 180 degrees, a relative positional relationship between a standing wave oscillation generated in the piezoelectric element and the projections is changed to thereby switch a direction of driving the ultrasonic motor.
In this case, when positive voltage is applied to the polarized portion, the polarized portion subjected to the polarizing treatment in positive polarity is elongated and the polarized portion subjected to the polarizing treatment in negative polarity is contracted. Further, when negative voltage is applied, the elongation and contraction relationship is reversed. That is, according to the ultrasonic motor of the invention, motor drive is carried out by standing wave oscillation generated at the piezoelectric element by inputting alternating voltage to all of the polarized portions of the piezoelectric element and there is constructed a constitution in which the polarized portions are divided in a multiple of four over the circumferential direction, a wave of one wavelength is generated in the peripheral direction of continuous four polarized portions, the first and the second polarized groups are constituted by selecting every other polarized portions and accordingly, by making the phase of alternating voltage inputted to the first and the second polarized portion groups to be the same phase or inputting alternating voltage having a phase difference of 180xc2x0, the positional relationship between the projections for taking out output and the standing wave oscillation generated at the piezoelectric element is changed and the direction of rotating the moving member can be switched. That is, the driving direction can be switched regardless of applying the voltage to all of the polarized portions provided to the piezoelectric element.
Therefore, there can be provided an ultrasonic motor increasing an output per unit volume in comparison with a conventional motor and capable of switching the driving direction.
Further, according to the present invention, there is provided an ultrasonic motor characterized in that in the above-described ultrasonic motor, alternating voltage is inputted to both the first polarized portion group and the second polarized portion group, standing wave oscillation having a node at the center of the piezoelectric element and having one node (one node circle) over the diameter direction is generated, the projections for taking out output each is disposed at a position at an upper portion at every odd number of the polarized portion and at a position in the diameter direction which is the position maximizing the oscillation amplitude between the center of the piezoelectric element and the node circle of the standing wave oscillation and disposed at a position in the circumferential direction which is at a center in the peripheral direction of the upper portion at every odd number of the polarized portions.
According to the invention, strong oscillation is excited in the piezoelectric element since standing wave oscillation having one node, that is, one node circle in the diameter direction is generated. Further, the projection for taking out output is disposed at the position maximizing the oscillation amplitude between the center of the piezoelectric element and the node circle of the standing wave oscillation as the position in the diameter direction and arranged at the center in the peripheral direction of the upper portion of the every other polarized portion in the peripheral direction and accordingly, oscillation energy can most efficiently be converted into drive force of the moving member and accordingly, an effect by the above-described invention is achieved and the ultrasonic motor having higher output can be provided.
Further, the invention is characterized in an ultrasonic motor according to the above-described ultrasonic motor, in which there is provided at least one of auxiliary projections for maintaining balance of oscillation which is formed to be lower than the projection for taking out output such that the auxiliary projections are not brought into contact with the moving member between the respective projections for taking out output.
According to the invention, when the projections for taking out output are provided at only a portion of the polarized portions of the piezoelectric element, the balance of the total of the piezoelectric element is deteriorated, however, according to the invention, by providing the auxiliary projections, the balance of the flexing standing wave oscillation generated by the piezoelectric element can be regulated and further stabilized high output can be provided. In this case, the auxiliary projection is lower than the projection for taking out output and is not brought into contact with the moving member and therefore, the-driving thereof is not hampered.
Further, the invention is characterized in that in the above-described ultrasonic motor, an elastic member in a circular disk shape bonded to the piezoelectric element is provided and the projections for taking out output and the auxiliary projections are integrally formed at the surface of the elastic member in the circular disk shape.
According to the invention, by providing the projections directly on the upper face of the piezoelectric element, fabrication thereof is facilitated and the projections can be provided further inexpensively.
Further, the invention is characterized in that in the above-described ultrasonic motor, the invention is provided with a self-excited oscillation drive circuit for driving the ultrasonic motor by generating alternating voltage inputted to the first and the second polarized portion groups by self-excited oscillation of the piezoelectric element, the self-excited oscillation drive circuit is constituted by a first noninverted power amplifier and a first inverted power amplifier, output terminals of which are connected to the first polarized portion group of the piezoelectric element, a second power amplifier (noninverted or inverted) an output terminal of which is connected to the second polarized portion group of the piezoelectric element and a motor control circuit for starting and stopping the motor and switching the rotational direction by bringing the first noninverted power amplifier, the first inverted power amplifier and the second power amplifier respectively into an active state or a nonactive state.
In this case, the motor drive is carried out by bringing either the first noninverted power amplifier or the first inverted power amplifier and the second power amplifier (noninverted or inverted) simultaneously into the active state. In this case, the direction of driving the ultrasonic motor can be switched by selecting the first noninverted power amplifier or the first inverted power amplifier.
According to the invention, the ultrasonic motor can be driven very simply and an ultrasonic motor having excellent way of use, being inexpensive and having high power can be provided.
Further, the invention is characterized in an ultrasonic motor having polarized portions divided by a multiple of two in the circumferential direction and comprising an oscillator having a piezoelectric element in a circular disk shape for generating standing wave by inputting same voltage to all of the polarized portions, projections provided to the oscillator and provided onto faces of the polarized portions of the piezoelectric element, a moving member brought into contact with the projections and driven by the projections and a self-excited drive circuit constituted by a power amplifier an output terminal of which is connected to the plurality of polarized portions and a motor control circuit for starting or stopping the motor by bringing the power amplifier into an active state or a nonactive state.
According to the invention, for use of one direction rotation, high output can be realized very inexpensively.
Further, the invention is characterized in that in the above-described ultrasonic motor, the self-excited oscillation drive circuit is provided with a condenser connected in series with the polarized portions provided to the piezoelectric element and an LC resonating circuit is constituted by induction performance provided when the piezoelectric element is brought into mechanical resonating state and the condenser to thereby drive the motor by bringing the piezoelectric element into self-excited oscillation.
According to the invention, there is constructed the constitution in which frequency selecting performance in the self-excited oscillation drive circuit is provided by the LC resonating circuit comprising the induction performance provided when the piezoelectric element is brought into the mechanical resonating state and the condenser and accordingly, the stable self-excited oscillation can be realized, as a result, there is provided the ultrasonic motor excellent in stability in addition to high output.
Further, the invention is characterized in that there is provided an electronic apparatus having the above-described ultrasonic motor as a drive force source (for example, analog time piece having the ultrasonic motor).
According to the invention, in comparison with the conventional ultrasonic motor, the ultrasonic motor having large output is used and accordingly, by further downsizing the ultrasonic motor, or by downsizing power transmission mechanism, electronic apparatus having the ultrasonic motor such as electronic time piece, measuring instrument, camera, printer, printing machine, machine tool, robot, moving apparatus, storing apparatus or the like can be downsized.